12/3/14 1 Cell Growth and Reproduction Cell Size Why are cells so small? Cells do not contain a circulatory system Cells receive nutrients and remove waste through diffusion Diffusion- movement of molecules from high concentration to low concentration until equilibrium is reached Diffusion occurs quickly over small distances, but very slowly over long distances The smaller the cell the quicker nutrients are spread through out the cell and waste is ejected
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Cell Growth and Reproduction
Cell Size � Why are cells so small? � Cells do not contain a circulatory system
� Cells receive nutrients and remove waste through diffusion � Diffusion- movement of molecules from high
concentration to low concentration until equilibrium is reached
� Diffusion occurs quickly over small distances, but very slowly over long distances � The smaller the cell the quicker nutrients are
spread through out the cell and waste is ejected
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Cell Size � The limiting factor of the cell is the surface area to
volume ratio � Example: a cube with dimensions of 10 x 10 x 10 � What is the surface area? (l x w x 6)
� 600
� What is the volume? (l x w x h) � 1000
� What is the ratio? � .6
Cell Size � Now imagine the cube doubled in size.
� 20 x 20 x 20 � What is the surface area?
� 2400
� What is the volume? � 8000
� What is the ratio? � .3
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Cell Division � Why do cells divide? � There are 3 very important reasons:
� Growth � Repair � Reproduction
� Growth � The larger an organism is the more cells it needs
to receive the nutrients and dispose of the waste
Cell Division � Repair
� Cells do not live forever, eventually each cell dies
� Replaced by new cells through cell division � Cells are small so that when they are
replaced, it doesn’t disrupt the whole organism. (Car parts)
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Cell Division � Reproduction
� To create offspring to keep the species going
� Two types: � Asexual reproduction carried out through
mitosis � Sexual reproduction carried out through
meiosis
Cell Cycle � How do cells know when to divide?
� Hormones from the organism signal the cell to start dividing
� All cells go through the first phase of growth and/or division � Interphase
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Cell Cycle � Interphase
� At this stage growth and preparation occur for cell division
� Three distinct stages � G1- The cell grows in size and develops � S- The nucleus begins to synthesize or copy
DNA. � Two identical copies of chromosomes are
produced � G2- organelles and other material are copied
or made
Cell Cycle � Mitosis
� There are 4 phases within the mitosis � Prophase � Metaphase � Anaphase � Telophase
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Cell Cycle � Prophase
� What is the difference between chromatin, chromatid, chromosomes?
� Chromatin condenses to form chromosomes
� Nuclear envelope disappears
� Centrioles form spindle fibers which connect to chromatids � Chromatids are single sides
of the chromosome � Centrioles move to
opposite ends of the cell
Cell Cycle � Metaphase
� Chromosomes line up along the equator of the cell
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Cell cycle � Anaphase
� Spinal fibers pull apart chromosome at the centromere
Cell Cycle � Telophase and Cytokinesis
� What do you think occurs during telophase? � New nuclear envelope forms around chromatid � Chromatids unwind into chromatin � Cytokinesis begins and pinches off new cell
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Cell Cycle � Meiosis
� What is the purpose of this type of cell division? � The formation of gametes through cell division in
reproductive cells
� Interphase still occurs before Meiosis begins � Broken down into Meiosis I and Meiosis II � Meiosis I has four stages
� Prophase I � Metaphase I � Anaphase I � Telophase I
Cell Cycle � Prophase I
� Same processes occur as in mitosis � Chromosomes are formed and the nuclear
envelope dissolves � The difference is that 2 chromosomes pair
up.
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Cell Cycle � Metaphase I
� Instead of each chromosome lining up in the middle, the pairs line up
Cell Cycle � Anaphase I
� The pairs of chromosomes are pulled apart
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Cell Cycle � Telophase I
� Nuclear envelope may or may not form
� cytokinesis occurs � Pairs of chromosomes are
contained within the newly formed cells
� At the end of cytokinesis, cell goes into Meiosis II
Cell Cycle � Meiosis II
� The cell cycle repeats and is the same as mitosis
� At the end of the telophase II there are 4 daughter cells called gametes � These cells only have half the number of
chromosomes as other cells
� There are many similarities to Meiosis and Mitosis: What are some of the differences?